This invention is concerned with a novel and improved method for preparing the antipsychotic and antidepressant drug, opipramol (I). More particularly, this invention is concerned with a novel method for converting iminostilbene (II), also known as dibenzo-[b,f]azepine, into N-(3-halopropyl)iminostilbene, a mixture of 3-chloro- and 3-bromopropyl derivatives, which is a precursor one step removed from opipramol (I).
In a preferred method of synthesizing opipramol (I), iminostilbene (II) is used as the starting material and is first alkylated with 1-bromo-3-chloropropane to yield N-(3-halopropyl)-iminostilbene (III), which is used in turn to alkylate N-(2-hydroxyethyl)piperazine at the secondary amine site to yield opipramol(I), as shown by the following equations, where X is chlorine or bromine. ##STR2##
According to German Patent 1133729, alkylation of iminostilbene (II) requires the use of a strong base catalyst, such as sodamide. Sodamide has been employed in non-aqueous media, to convert iminostilbene (II) into its anion (V) , which may then be alkylated, a shown by the equations below. ##STR3##
where R is lower alkyl and X is halogen, preferably Br.
When R is free of base-sensitive groups, such a procedure is effective and efficient. However, when 1-bromo-3-chloropropane is the alkylating reagent, the desired product, N-(3-halopropyl)-iminostilbene (III) is converted by the strongly basic medium, at least in part, to the illustrated dehydrohalogenated by-product, N-allyl-iminostilbene (IIIa), which is unsuitable for direct conversion to opipramol (I).